(a) Field of the Invention
An exemplary embodiment of the present invention relates to a power supply device implemented by a buck converter, a driving method of the power supply device, and a switch controller applied to the power supply device.
(b) Description of the Related Art
FIG. 1 is a circuit diagram illustrating a conventional low-side buck converter for driving an LED string.
As shown in FIG. 1, AC power source AC is rectified by passing through a bridge diode 1. The bridge diode 1 full-wave rectifies the AC power source AC. The rectified voltage, that is, an input voltage is supplied to an inductor 2 through an LED string, and the inductor 2 supplies a driving current to the LED by an operation of a power switch S. A switching unit 3 including the power switch S controls a switching operation of the power switch S.
When the power switch S is turned-on, a LED current flowing through the LED string is increased. When the power switch S is turned-off, the LED current is reduced.
The switching unit 3 according to the conventional art controls a switching operation according to a peak of a current flowing through the power switch S. Since a current flows through a diode 4 in the LED string at an off period of the power switch S, a scheme of controlling only a peak of a current flowing through the power switch S has a limitation on Constant Current (CC) control.
Further, sub-harmonic may be prevented in a current control mode by limiting a switching duty to be 50% or less or performing slope compensation. The slope compensation refers to varying a slope of a control signal for controlling a peak current flowing through the power switch. Then, there is a need for a complex circuit to limit a switching duty or to perform the slope compensation.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.